Assessment of the fetus during pregnancy, and particularly during labor and delivery, is an essential yet elusive goal. While most patients will deliver a healthy child with or without monitoring, more than 5 out of every 1,000 deliveries of a viable fetus near term are stillborn, with half having an undetermined cause of death. (National Vital Statistics System (NVSS), CDC, NCHS as published in “Healthy People 2010, Understanding and Improving Health: Chapter 16,” co-authored by the Centers for Disease Control and Prevention and Health Resources and Services Administration, 2nd Edition, U.S. Government Printing Office, November 2000). The risk of this unfortunate consequence is increased in a subgroup of “high risk” patients (e.g., diabetics). In addition to regular obstetric observation, after 23 weeks gestation antepartum (“in utero”) fetal monitoring consists of the following (in order of complexity):                1. maternal report of fetal movement;        2. non-stress test (NST)—monitor fetal heart rate (FHR) by ultrasound, looking for baseline rate, variability and presence of accelerations above the baseline;        3. contraction stress test (CST)—response of the FHR to uterine contractions, either natural or induced; and        4. biophysical profile (BPP)—NST plus ultrasonographic evaluation of fetal movements and amniotic fluid volume.        
Despite their wide acceptance, these tests offer limited predictive value, and give only a glimpse of the fetus at the time of testing. For high risk patients, once or twice weekly surveillance is often indicated, entailing both expense and inconvenience for the patient.
Intrapartum fetal surveillance is accomplished routinely with intermittent auscultation or continuous Doppler monitoring of the FHR, together with palpation or tocodynamometry (strain gauge) monitoring of contractions. When indicated, more invasive monitors are available, but require ruptured membranes/adequate cervical dilation, and entail some risk, primarily infectious. These monitors include, without limitation:                1. fetal scalp electrode—a wire electrode inserted into the fetal scalp;        2. intra-uterine pressure catheter (IUPC)—enables quantitative measurement of contractions; and        3. fetal scalp sampling—a blood sample drawn for pH analysis.        
Contraction detection allows monitoring of the progress of labor. A device commonly used in monitoring contractions is the tocodynamometer. The tocodynamometer detects physical changes in the curvature of the mother's abdomen (usually with a strap or belt that is placed about the abdomen) during a contraction and translates these changes into a printed curve. The tocodynamometer detects only the presence or absence of tension on the abdomen (whether from uterine contraction or maternal movement), and often fails in the presence of obesity. Unfortunately, patients are recommended to remain in a supine position when using a tocodynamometer to monitor labor, which has been found to be the least effective physiological position for encouraging fetal internal rotation and often causes maternal hypotension and discomfort.
When cervical dilation lags behind the anticipated labor curve, oxytocin is often indicated to induce a more effective contraction pattern. Safe titration of the oxytocin may require accurate determination of “montevideo units” which measure the strength of uterine contractions over 10 minutes. This requires the more invasive IUPC, a catheter placed into the uterus, alongside the fetus, to measure the pressure generated by uterine contractions.
The rationale for use of intrapartum electronic fetal monitoring (EFM) assumes that FHR abnormalities accurately reflect hypoxia (inadequate oxygen to the fetus), and that early recognition of this could induce intervention to improve outcome for both mother and fetus. Unfortunately, numerous studies have failed to identify this improved outcome with the use of EFM in low-risk deliveries. In fact some studies have actually shown an increase in morbidity from a higher operative delivery rate. Perhaps this should not be surprising in light of the variability in interpretation of FHR tracings and their lack of specificity for hypoxia. Yet, continuous EFM remains the standard of care in US hospitals, in large part due to medical and legal concerns.
Uterine contractions are the result of the coordinated actions of individual myometrial cells. At the cellular level, the contractions are triggered by a voltage signal called an action potential. During pregnancy, cellular electrical connectivity increases such that the action potential propagates to produce a coordinated contraction involving the entire uterus. The action potential during a uterine contraction can be measured with electrodes placed on the maternal abdomen resulting in a uterine EMG signal (hereinafter referred to as “EHG”: electrohysterogram). Specifically, the EHG signal can be processed to produce a signal that is similar to the standard uterine activity signal from the tocodynamometer or IUPC. The EHG provides contraction frequency and duration information. To date, EHG signals have not been used in assessing the intra-uterine pressure or predicting montevideo units.
Postpartum, continuous uterine contraction is required to minimize uterine bleeding from the placental detachment site. Hemorrhage is the leading cause of peripartum maternal death, and most of these are postpartum hemorrhage due to this “uterine atony.” Current monitoring consists of serial uterine palpation at intervals of several hours. Diagnosis is usually made by patient complaint of severe bleeding, or hypovolemic shock (from hemorrhage). Neither IUPC nor tocodynamometer monitoring is available at this time. The EHG would provide a unique means for monitoring the uterine tone, providing an early warning of atony and potential hemorrhage.
Devices that utilize invasive techniques for monitoring fetal health include those disclosed in U.S. Pat. Nos. 6,594,515; 6,115,624; 6,058,321; 5,746,212; 5,184,619; 4,951,680; and 4,437,467.
Accordingly, a cost-effective, more reliable system and method for non-invasively measuring uterine activity, in particular contractions during labor, without the need for expensive equipment replacement would be beneficial.